The TD is slightly better. However the Medallion compression is pretty low. It starts and runs then slows. Easily stalls when slows down. I'm in the process of trying to track down an improved cylinder for both of the old relics. So far not but am looking. Question I have. With lower compression is it usually only the cylinder that has wear? Or does the Piston also wear out. I've fixed a couple .020 that were fixed with just the cylinder replacement. Might the .09 also only need the cylinder changed?

How much prop are you tasking it to swing and how much castor oil are you using to keep the steel on steel heater cooled? Castor helps add compression when the engine is hot andreduces wear greatly retaining precious compression.

Have you reset the piston and rod with an .09 tool ?At TDC, with the head off and a prop attached, if the prop can be moved more than 2 or 3 degrees either direction without the piston moving, then it must be reset.It might feel good and tight but only a few degrees turning without movement will affect your engine performance.Before I got the entire reset tool set, I very carefully reset a TD.09 with a .049/.051 tool with great results.The key word is CAREFULLY.

Yea man i hope u get the reset done and FIND those gaskets , i know how it is sometimes with too much stuff!! I think with a reset and 2 new head gaskets , Good Hot plug , 7X3-4 P prop it should come alive . Let us know

Well I reset the piston lightly and took any slop out of it. I don't have any more of the head gaskets I only have a single one that is in the motor. All mine are for either .049 .020 or .010. I polished the head gasket and replaced all. It doesn't feel like it has any more compression but I will try it later tonight. I'll let you know.

A slight help may be provided by using a devarnisher brush: by advancing it through the cylinder swirling/rotating it like a bolt and definitely not pushing through the cylinder (that would leave unwanted longitudinal scratches) some fine circumferential marks are "scratched" into the liner wall that will retain the castor for better sealing. (Like the honing marks in a new cylinder) . Use it with caution, running it through only once or twice at a time, because excessive use will have the opposite effect..

A brass gun brush will do.. I bought mine in a gunshop...the size matches the 09 cylinder.

ok I've cross hatch scratched the cylinder as well with a pipe brush similar to the gun cleaning brush shown in the picture. I'll give a run later tonight. It might seem just a skosh more compression than before. I hope that the wear in run will improve even more.

Sorry for that Ice..it looks like your cylinder has really been used up to its useful lifetime. I do not think the cross-wise de-varnishing marks will add to the compression loss. More to the contrary, these are considered to strengthen the oil film adherence to the surface and thus retain compression a bit. I have a fairly used 09 cylinder. If you pm me your postal address I will send it to you free.

Do you mean the gasket itself or the gasket surface of the head? I really think you're going to need to fit a new gasket or two. Old gaskets compress and harden so that they no longher conform to the surface, causing a leak.Also, I know there are people who recommend sanding the head surface flat. Flat is good, but there is always the danger that the surface will end up being not perpendicular to the threads of the head. A slight misalignment may be overcome with a couple of new soft gaskets.

I sadly only have a single copper gasket for the .09. I have about 100 for .049 but not for .09. Is there anyway I can cut and use the .049 ones and carefully lay them at the lip at the top? Or is there another material or way to add additional shims or head gaskets (the copper ones)?

I sadly only have a single copper gasket for the .09. I have about 100 for .049 but not for .09. Is there anyway I can cut and use the .049 ones and carefully lay them at the lip at the top? Or is there another material or way to add additional shims or head gaskets (the copper ones)?

ThanksIce

I have heard of people cutting gaskets from aluminium drink cans, although I imagine this would be very difficult and I am unsure whether the thickness would be adequate.

Trying to use the .049 gaskets will not work- cutting them will never allow them to seal.

The bore-brush would not remove any material. As Balogh has said, any circumfrential scratches in the bore should assist the compression. Sounds to me like the removal and refit of the head gasket is what has reduced your compression following the bore clean.

If you have no other options apart from reusing your original gasket, maybe you can use some RTV automotive sealant on the gasket and in the threads of the head. Let it cure overnight before putting it under pressure.

Ultimately, the only way to properly solve the problem is to fit a new correct gasket.

Iceberg wrote:Hi BaloghMaybe check your inbox. It might be full and needing some messages deleted or something?? seems I can't send anything to you?

ThanksIce

Hi Darren,

as per the underlying pm messaging, the envelope has been sent to you with the complete, though used, top-end 09 overhaul set..as to the compression loss, I know it is a no-brainer, but putting a few drops of fuel in between the head and cylinder fins then driving the piston up will tell and show you in the shape of bubbles if the culprit is the worn head gasket, or, worse, the cylinder/piston fit.

Personally I suggest you acquire stocks of gaskets for ALL your Cox engines-I always keep at least half a dozen of each size from .010 to .15 in my spares box-sooner or later you need them-and they are not expensive. From time to time you will need additional gaskets to adjust head clearance to compensate for a fuel change or atmospheric conditions, or a non OEM head....